A condenser microphone includes a diaphragm configured to vibrate in response to acoustic waves from a sound source and a fixed electrode constituting a capacitor between the fixed electrode and the diaphragm. The capacitance of the capacitor varies in response to the vibration of the diaphragm. The condenser microphone outputs audio signals corresponding to the variation in the capacitance of the capacitor. The audio signals are output to an external device, such as a mixer or a speaker, connected to the condenser microphone.
The condenser microphone can be set to have various directionalities. One of the directionalities is unidirectivity. A unidirectional condenser microphone (hereinafter, referred to as “microphone”) collects acoustic waves in a specific direction (for example, the front direction).
FIG. 5 is a cross-sectional right view of a conventional microphone.
A microphone M collects acoustic waves from the sound source. The microphone M includes a microphone case M10, a microphone unit M20, a cord bush M30, a microphone cord M40, and a metal mesh M50.
The front of the microphone M is the direction of the microphone M directed to the sound source during sound collection (the left in FIG. 5). The rear of the microphone M is the direction opposite to the front of the microphone M (the right in FIG. 5).
The microphone case M10 accommodates the microphone unit M20, the front end of the microphone cord M40, and the metal mesh M50. The microphone case M10 is composed of metal, such as brass alloy, for example. The microphone case M10 has a shape of a hollow cylinder with a bottom end. The microphone case M10 has a front sound hole M11h and rear sound holes M12h. The front sound hole M11h introduces acoustic waves from the sound source into the microphone case M10. The front sound hole M11h is disposed in the bottom end (the front face) of the microphone case M10. The rear sound holes M12h introduce acoustic waves from the sound source to the interior of the microphone case M10. The rear sound holes M12h are disposed in the circumferential surface of the microphone case M10.
The microphone unit M20 outputs audio signals corresponding to the acoustic waves from the sound source.
The cord bush M30 prevents breaking of the microphone cord M40. The cord bush M30 is composed of elastic material, such as rubber. The cord bush M30 has a shape of a cone. The cord bush M30 has an insertion hole M31h. The insertion hole M31h extends along the central axis of the cord bush M30. The microphone cord M40 passes through the insertion hole M31h. 
The microphone cord M40 is connected to the microphone unit M20 and an external device (not shown), such as a speaker, for example. The microphone cord M40 is a two-core shielded cable including a power cable M41, a signal cable M42, and a shielded cable (not shown). The power cable M41 supplies electrical power to the microphone unit M20. The signal cable M42 outputs the audio signals from the microphone unit M20 to the external device. The shielded cable is grounded. In FIG. 5, the shielded cable is aligned with the power cable M41 and thus is not shown.
The metal mesh M50 prevents foreign objects and electromagnetic waves from entering the microphone case M10. That is, the metal mesh M50 constitutes a part of an electromagnetic shield that prevents electromagnetic waves. The metal mesh M50 is a plain-woven mesh composed of metal, such as stainless steel, for example.
The metal mesh M50 is accommodated in the microphone case M10 together with the microphone unit M20 and the front end portion of the microphone cord M40 connected to the microphone unit M20. The metal mesh M50 is attached to the inner circumferential surface of the microphone case M10 and covers the rear sound holes M12h from the inside of the microphone case M10. The cord bush M30 fits to the opening of the microphone case M10 and covers the opening of the microphone case M10 from the rear. The microphone case M10 is fixed to the cord bush M30 with a screw.
Due to the current widespread use of mobile phones, microphones sometimes receive intense electromagnetic waves from mobile phones. When electromagnetic waves intrude into the microphone case, the microphone may generate noise.
Schemes have been proposed to prevent intrusion of electromagnetic waves into a microphone case from a sound hole with a metal mesh covering the sound hole of the microphone case and constituting a part of an electromagnetic shield (for example, refer to Japanese Unexamined Patent Application Publication No. 2011-176613).